Arbritrary doping profiles in semiconductors with depth control to a few monolayers and exact control of n- and p- dopant levels to a few percent with no diffusional smearing are needed to fabricate new devices. Such doping profiles will, in many instances, be "hyperabrupt;" that is, having extreme profile changes. Examples of such devices are triangular barrier diodes, high-speed logic switches, mixers, fast photodiodes, BARITT devices and thermionic emission transistors.
Presently known doping methods used to achieve arbitrary profiles have primarily involved molecular beam epitaxy (MBE). With conventional MBE, silicon is doped either by evaporating antimony (n) or gallium (p), or by directing low-energy ionized beams of boron or arsenic into the growing silicon surface held at 700.degree.-900.degree. C. Evaporative doping suffers from low sticking coefficients, extreme temperature sensitivity, and transient smearing effects. Ion embedding is likewise cumbersome, and the resultant damage must be carefully annealed out. As yet, neither method has demonstrated good mobility at doping levels higher than 5.times.10.sup.18 cm.sup.-3 in either p- or n-type material.
Solid phase epitaxy (SPE), involving regrowth of deposited amorphous semiconductors with coevaporated dopants from either doped semiconductor sources or separate dopant sources, is known in the art. Such techniques, however, have not been successfully applied to the growth of semiconductor layers with arbitrary profiles, and in particular have not been successfully applied to produce hyperabrupt profiles. A technique which could successfully produce hyperabrupt junctions would find wide commercial applicability.
Accordingly, it is a principal object of the present invention to achieve hyperabrupt doping profiles in semiconductors.
It is another object of the present invention to achieve such profiles utilizing SPE regeneration of doped amorphous films.
Yet another object of the present invention is to utilize SPE to produce hyperabrupt junctions with: no smearing, unity sticking coefficients, greater than solid solubility limits, good electrical mobility, and good crystal quality.
A further object of the present invention is to allow arbitrary dopant control to a few atomic layers.